1. Field of the Invention
The present invention relates to an a.c. generator for vehicle, which is driven by an internal combustion engine of a vehicle.
2. Discussion of Background
When an a.c. generator for vehicle is run, in order to ensure best function, it is necessary to cool an entire generator to be in a certain limit temperature or less. As a method of cooling, a fan is fixed to a disk of a magnetic pole wheel of a rotor and arranged inside a casing so as to be opposite to a winding wire of a stator to dissipate a sufficient heat quantity. Accordingly, a degree of cooling is improved, and an output from the a.c. generator can be increased. However, there is a problem that a large wind noise is generated by a turbulent flow of an air inside the casing. In order to solve this problem, the following has been proposed in a conventional technique.
FIG. 14 illustrates a cross-sectional view of a conventional a.c. generator for a vehicle disclosed in, for example, Japanese Unexamined Patent Publication JP-A-5-161286. FIG. 15 is a perspective view of a magnetic pole wheel of a rotor of the a.c. generator illustrated in FIG. 14. FIG. 16 illustrates an end surface of the magnetic pole wheel illustrated in FIG. 15 viewed in a direction of an arrow F in FIG. 14. FIG. 17 is a cross-sectional view taken along a line Ixe2x80x94I illustrated in FIG. 16. FIG. 18 is an enlarged view of one of teeth of the magnetic pole wheel.
The a.c. generator has a stator assembly having stator core 4, formed by laminating metallic thin plates and having a plurality of grooves accommodating stator winding wires 5. The stator assembly is retained between a front bracket 1 and a rear bracket 2, which are mutually joined by bolts.
A rotor assembly, including two claw-type magnetic pole wheels 8 and 9, is mounted on a rotational shaft 7, wherein a central rotor core (not shown) having induction winding wires is retained between the magnetic pole wheels 8 and 9. The rotor assembly is engaged with, for example, a spline (not shown) formed in the rotational shaft 7 so as to rotate along with the rotational shaft 7.
Ends of the induction winding wires are connected to hollow connectors 26 and 27. The connectors 26 and 27 are respectively connected to corresponding one of two slip rings 14, respectively being in contact with corresponding one of two brushes 15 through the rotational shaft 7.
On back surfaces of the magnetic pole wheels 8 and 9, cooling fins 11 and 12 are respectively fixed. The magnetic pole wheels 8 and 9 respectively have a disk 50 in perpendicular to an axis line of the rotational shaft 7. In central portions of the disks 50, a concentric through-hole 51 for inserting the rotational shaft 7 is formed. On outer peripheral edges of the disks 50, six magnetic pole teeth 52 are monolithically formed. The teeth 52 are arranged with equal intervals, which are inwardly directed toward the other magnetic pole wheel and substantially in parallel with the axis line of the rotational shaft.
The teeth 52 of the magnetic pole wheel 8 are shifted by 30xc2x0 in their peripheral direction with respect to the teeth 52 of the magnetic pole wheel 9. The teeth of the magnetic pole wheels are mutually inserted between the opposite teeth. As illustrated in FIG. 15, the magnetic pole wheels are shaped like angular magnetic pole crowns having opened ends. Polarities of the magnetic pole teeth 52 of the magnetic pole wheel 8 and of the magnetic pole teeth 52 of the magnetic pole wheel 9 are mutually adverse, wherein consecutive magnetic pole openings, having polarities adverse to those of grooves of the stator of the a.c. generator, are formed.
As illustrated in FIGS. 15 through 18, the magnetic pole teeth are shaped like a trapezium when viewed in a direction of the stator. Wide base portions of the teeth are joined to the disks 50 of the magnetic pole wheels. In more detail, the teeth 52 are formed by a cylindrical outer surface 54, chamfered portions 57 and 59, and two types of side surfaces 56 and 58, joined to the outer surfaces 54.
In directions perpendicular to the disks 50, the side surfaces 56 and 58 are in parallel with axis of symmetry Xxe2x80x94X of the teeth 52. In regions apart from the disks 50, the side surfaces 56 and 58 are slanted so as to symmetrically converge into the axis Xxe2x80x94X, and joined via the end surface 60, forming an end portion of the teeth 52 and being in perpendicular to the axis Xxe2x80x94X. The outer surface 54 is joined to the back surface 62 of the disk 50 via a slant surface 64.
The teeth 52 respectively have at least one chamfered portion 66, functioning to prevent a noise. The chamfered portion is adjacent to the outer surface 54, and the side surfaces 56 or 58 on one side, and is adjacent to the surface 64 and surface 62. The chamfered portions 66 for preventing noise are slanted by angles respectively different from degrees of slant of the adjacent surfaces.
However, in the conventional a.c. generator for vehicle, there is a problem that an output is decreased because the chamfered portions 66 are too large. FIG. 19 is a cross-sectional view of a part of the conventional a.c. generator for vehicle, wherein a flow of a magnetic flux is shown. As designated by an arrow in FIG. 19, the flow of the magnetic flux "PHgr" forms a loop from the magnetic pole wheel 8 of the rotor, the stator core 4, again the rotor, and the magnetic pole wheel 9 of the rotor, to the magnetic pole wheel 8. If the chamfered portion 66 of the magnetic pole wheel 8 or 9 is increased, the length 1 of a shoulder portion of the magnetic pole wheel 8, through which the magnetic flux "PHgr" passes, is shortened. Accordingly, a cross-sectional area of the magnetic pole wheel 8 is reduced, therefore the magnetic flux "PHgr" can not sufficiently pass, whereby there are problems that a property of the magnetic circuit is deteriorated, and an output is reduced.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide an a.c. generator for vehicle, which can reduce noises such as a wind noise and an electromagnetic noise, and can improve a magnetic circuit of a rotor so as to increase a magnetic flux to obtain a high output.
According to a first aspect of the present invention, there is provided an a.c. generator for a vehicle comprising:
a stator core having a stator coil;
a first rotor core, fixed to a rotational shaft inside an inner diameter of the stator core;
a second rotor core, fixed to the rotational shaft inside the inner diameter of the stator core;
a field magnetic coil for magnetizing the first rotor core and the second rotor core; and
a plurality of first magnetic pole pieces and a plurality of second magnetic pole pieces, which are located in an axis direction of the rotational shaft respectively from the first rotor core and the second rotor core so as to mutually engage with a predetermined gap and to be opposite to the inner diameter of the stator core with a predetermined gap,
wherein at least the first magnetic pole pieces or the second magnetic pole pieces has chamfered portions, formed by a surface on three points, being a point on a most outer periphery of a root shoulder portion and on a taper continuing from the most outer periphery toward an outer side of the generator in the axis direction to an end surface of the stator core, a point on a skew slanted portion of the magnetic pole piece, and a point on a surface of the magnetic pole piece apart from the end surface of the stator core by a distance between L1/4 and 7xc3x97L1/8 in the axis direction, where L1 is a distance between a root end surface of the magnetic pole piece and the end surface of the stator core.
According to a second aspect of the present invention, there is provided the a.c. generator for vehicle according to the first aspect of the present invention, wherein the chamfered portions are formed on both of the first and second magnetic pole pieces.
According to a third aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein the chamfered portions are formed on the peripheral end surfaces on both sides of the root shoulder portion.
According to a fourth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects, wherein the point on the skew slanted portion of the magnetic pole piece is positioned where tip ends of teeth of the stator core are overlapped in radial directions.
According to a fifth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects,
wherein the distance between the end surface of the stator core and the point on the skew slanted portion of the magnetic pole piece is a distance between the end surface of the stator core and a cross point between the tip end of the teeth of the stator core and the skew slanted portion of the magnetic pole piece or less.
According to a sixth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects, wherein a distance between two of the points on the taper of the root shoulder portions and also on two of the chamfered portions is a half of a width of the magnetic pole piece in the peripheral directions or less.
According to a seventh aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects, wherein the number of the slots of the stator core is two by each pole and each phase.
According to an eighth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein the chamfered portion is formed by a curved surface.
According to a ninth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein the chamfered portions and surfaces adjacent thereto are joined so as to form a rounded shape.
According to a tenth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein the point on the taper in the root shoulder portion of the magnetic pole piece is substantially aligned in the axis direction with the end surface of the stator core.
According to an eleventh aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein widths of adjacent teeth of the stator core are different each other.
According to a twelfth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein an annular fan is located on at least one of end surfaces of the first rotor core and the second rotor core, and an outer diameter of the fan is smaller than that of the first rotor core or the second rotor core.
According to a thirteenth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects of the invention, wherein the stator coil has a coil end outwardly extending from the end surface of the stator core, and a shielding plate is located thereto to shield at least an inner peripheral surface of the coil end.
According to a fourteenth aspect of the present invention, there is provided the a.c. generator for vehicle according to the preceding aspects, wherein the stator coil has a coil end outwardly extending from the end surface of the stator core, and the coil end is arranged by aligning the stator coil in peripheral directions.